Thats a fantastic idea as long as they can speak perfect english, Firstly though it would make sense to get the feral lazy underclass of britain to join first and beat some self respect into them and get them contributing to the economy.
National Service or forced labour or we could gas them :)
IMHO linguistic skills should not be a deciding factor
Communication is of the upmost importance in the armed forces - lack of said communication can cause death! I'm actually amazed at the stupidity of that comment. It's quite aparent you've never actually worked in a job where people depend on good lines of communication to keep them alive!
In my personal opinion, I don't think that Poles should be able to join the British army, why the hell would they want to anyway? I wouldn't expect none British person to put their life on the line for my country - most people don't even want to do it for their own!